1. Field of Invention
The invention relates to a piezoelectric vibration gyro element including a driving resonant arm and a detecting resonant arm, a method for manufacturing the same, and a piezoelectric vibration gyro sensor using the same.
2. Description of Related Art
Piezoelectric vibration gyroscopes have been widely used in a rotation angle velocity sensor for ship, aircraft, automobile attitude control and navigation systems and the sensor for detecting and preventing the movement of camcorders, and in a rotation direction sensor for three-dimensional mice. Various configuration types have been proposed for serving as such piezoelectric vibration gyroscopes. Examples of these include rotation velocity sensors having fork-shaped parts on both sides (e.g., Japanese Unexamined Patent Application Publication No. 7-55479), and so-called double T-shaped piezoelectric resonators having substantially T-shaped driving resonant systems laid out symmetrically about a central detecting resonant system (e.g., Japanese Unexamined Patent Application Publication No. 2003-166828 and Japanese Unexamined Patent Application Publication No. 2001-12952).
FIGS. 11(A) through (C) show an example of a double T-shaped piezoelectric vibration gyro element. As shown in FIG. 11(A), a piezoelectric vibration gyro element 1 is laid out horizontally. The piezoelectric vibration gyro element 1 can include a pair of detecting resonant arms 3, 3, a pair of connecting arms 4a, 4b, and right and left pairs of driving resonant arms 6a, 6a, 6b, 6b. The detecting resonant arms 3, 3 extend from a central supporting part 2 upward and downward in the drawing. The connecting arms 4a, 4b extend from the central supporting part 2 to the right and left in the drawing in a direction perpendicular to the detecting resonant arms. The driving resonant arms 6a, 6a, 6b, 6b extend from bases 5a, 5b, which are the far ends of the connecting arms, upward and downward in the drawing in parallel with the detecting resonant arms.
As shown in FIG. 11(B), each of the detecting resonant arms is provided with a first detecting electrode 7 and a second detecting electrode 8 on its front and back main surfaces and both sides, respectively. As shown in FIG. 11(C), each of the driving resonant arms is provided with a first driving electrode 9 and a second driving electrode 10 on its front and back main surfaces and both sides, respectively.
When applying alternating current to the driving electrodes via an electrode pad above the central supporting part 2, the driving resonant arms 6a, 6a, 6b, 6b flexural vibrate in the XY plane including their main surfaces in the direction indicated by arrows. When the piezoelectric vibration gyro element 1 rotates in the XY plane, i.e., around the Z axis, in this state, the Coriolis force arises along the longitudinal direction of the driving resonant arms back and forth alternately, making the connecting arms 4a, 4b also flexural vibrate in the XY plane in the direction indicated by arrows. The force is transmitted via the central supporting part 2, and thereby making the detecting resonant arms 3, 3 also flex and vibrate in the XY plane in the direction indicated by arrows. The detecting electrodes detect the distortion of piezoelectric material due to the detecting resonant arms' flexure and vibrating and generate a signal. By electrically processing the signal, the rotation and angle velocity in the plane around the Z axis are measured.
Japanese Unexamined Patent Application Publication No. 2001-12952 also discloses the following configuration of such a double T-shaped piezoelectric resonator. According to the document, extension parts 11a, 11b are provided to the end of a supporting part (corresponding to the bases 5a, 5b referring to the ends of the connecting arms 4a, 4b in FIG. 11(A)), toward the extension of the supporting part (corresponding to the connecting arms 4a, 4b) as indicated by imaginary lines in FIG. 11(A). Also, tapered parts 12a, 12a, 12b, 12b are provided on each side surface of the extension parts 11a, 11b adjacent to the driving resonant arms, like at the base of each detecting resonant arm and of each connecting arm extending from the central supporting part 2, and each junction between the driving resonant arm and the connecting arm. These extension parts and tapered parts enhances the symmetry of the driving resonant arms' flexure and vibrating, and thereby reducing variations in the vibration state due to temperature fluctuations. This eventually reduces resonance frequency drift resulting from the ambient temperature.
FIG. 12 shows one of the driving resonant arms 6a, 6b included in a double T-shaped configuration. Typically, the first driving electrodes 9, 9 formed on the front and back main surfaces are coupled each other with an electrode film 13 provided at the end of the connecting arm 4a (4b) therebetween. Meanwhile, the second driving electrodes 10, 10 and the electrode film 13 are separated on the side surface of the driving resonant arm 6a (6b) and the end surface of the connecting arm 4a (4b), i.e., the side surface of the base 5a (5b), all of which are on the same plane.
Various methods have been proposed in order to separate electrodes on the side surface of such a piezoelectric resonator. Example of these include a method for providing an electrode film on the surface of a tuning fork-shaped thin crystal plate and then mechanically cutting off a projection provided at the part of separation of side electrodes in advance, and a method for partly removing such an electrode film by irradiating a portion of separation of side electrodes with a laser (e.g., Japanese Unexamined Patent Application Publication No. 54-29596). Another example is a method for exposing recessed parts provided to a part of separation of side electrodes in such a piezoelectric resonator to perpendicular light and then etching a conductive thin film in the recessed parts in order to separate the side electrodes (e.g., Japanese Unexamined Patent Application Publication No. 59-104813). Also, the same can be achieved by a method for forming an electrode film on the front and back main surfaces and side surfaces of a crystal element by means of vacuum deposition using a deposition mask having a window for electrode patterning (e.g., Japanese Unexamined Patent Application Publication No. 8-23249).
An alternative method is forming an electrode film on the whole surface of a shaped piezoelectric resonator, depositing a photoresist film on the electrode film, exposing the film by using masks for electrode patterning, and then wet etching the electrode film, so as to form electrodes and provide a wiring on the front and back main surfaces and side surfaces of the piezoelectric resonator (e.g., Japanese Unexamined Patent Application Publication No. 2003-218657). In separating side electrodes using photo etching, the front and back main surfaces and side surfaces can be separately exposed using different exposure masks or exposed all at once from the above in an oblique direction using a single exposure mask (see, Japanese Unexamined Patent Application Publication No. 59-104813 and Japanese Unexamined Patent Application Publication No. 2003-218657). While it becomes comparatively difficult to separate side electrodes with smaller piezoelectric resonators according to the above mentioned methods disclosed in Japanese Unexamined Patent Application Publication No. 54-29596 and Japanese Unexamined Patent Application Publication No. 8-23249 as the trend toward compact equipment develops, the separation of side electrodes using photo etching has an advantage of providing a solution to smaller piezoelectric resonators.